The invention relates to transcutaneous immunization, and adjuvants useful therein, to induce an antigen-specific immune response.
Transcutaneous immunization requires both passage of an antigen through the outer barriers of the skin, which are normally impervious to such passage, and an immune response to the antigen. We showed in U.S. application Ser. No. 08/749,164 that using cholera toxin as an antigen elicits a strong antibody response that is highly reproducible; the antigen could be applied in a saline solution to the skin, with or without liposomes. In the present application, we show transcutaneous immunization using adjuvants such as, for example, bacterial exotoxins, their subunits, and related toxins.
There is a report of transdermal immunization with transferosomes by Paul et al. (1995). In this publication, the transferosomes are used as a carrier for proteins (bovine serum albumin and gap junction proteins) against which the complement-mediated lysis of antigen-sensitized liposomes is directed. An immune response was not induced when solution containing the protein was placed on the skin; only transferosomes were able to transport antigen across the skin and achieve immunization. As discussed in U.S. application Ser. No. 08/749,164, transferosomes are not liposomes.
FIG. 1 of Paul et al. (1995) showed that only a formulation of antigen and transferosomes induced an immune response, assayed by lysis of antigen-sensitized liposomes. Formulations of antigen in solution, antigen and mixed micelles, and antigen and liposomes (i.e., smectic mesophases) applied to the skin did not induce an immune response equivalent to that induced by subcutaneous injection. Therefore, there was a positive control (i.e., antigen and transfersomes) to validate their negative conclusion that a formulation of antigen and liposomes did not cause transdermal immunization.
Paul et al. (1995) stated on page 3521 that the skin is an effective protective barrier that is "impenetrable to substances with a molecular mass at most 750 DA", precluding non-invasive immunization with large immunogen through intact skin. Therefore, the reference would teach away from using a molecule like cholera toxin (which is 85,000 daltons) because such molecules would not be expected to penetrate the skin and, therefore, would not be expected to achieve immunization. Thus, skin represents a barrier that would make penetration by an adjuvant or antigen like cholera toxin unexpected without the disclosure of the present invention.
Paul and Cevc (1995) stated on page 145, "Large molecules normally do not get across the intact mammalian skin. It is thus impossible to immunize epicutaneously with simple peptide or protein solutions." They concluded, "The dermally applied liposomal or mixed micellar immunogens are biologically as inactive as simple protein solutions, whether or not they are combined with the immunoadjuvant lipid A."
Wang et al. (1996) placed a solution of ovalbumin (OVA) in water on the skin of shaved mice to induce an allergic type response as a model for atopic dermatitis. Mice were anesthetized and covered with an occlusive patch containing up to 10 mg of OVA, which was placed on the skin continuously for four days. This procedure was repeated after two weeks.
In FIG. 2 of Wang et al. (1996), an ELISA assay done to determine the IgG2a antibody response showed no IgG2a antibody response to OVA. However, IgE antibodies that are associated with allergic responses could be detected. In a further experiment, the mice were more extensively patched with OVA in solution for four days every two weeks. This was repeated five times, i.e., the mice wore patches for a total of 20 days. Again, the high dose of OVA did not produce significant IgG2a antibodies. Significant levels of IgE antibodies were produced.
The authors stated on page 4079 that "we established an animal model to show that epicutaneous exposure to protein Ag, in the absence of adjuvant, can sensitize animals and induce a dominant Th2-like response with high levels of IgE". Extensive epicutaneous exposure to high doses of protein antigen could not produce significant IgG antibodies but could induce IgE antibodies, the hallmark of an allergic type reaction. Thus, Wang et al. (1996) teaches that OVA exposure as described is a model for atopic dermatitis and not a mode of immunization. Therefore, following the teaching of the reference, one would have expected that transcutaneous immunization with antigen would induce high levels of IgE antibodies if it were to pass through the skin and induce an immune response. Instead, we have unexpectedly found that antigen placed on the skin in a saline solution with adjuvant induces high levels of IgG and some IgA, but not IgE.
In contrast to the cited references, the inventors have found that application to the skin of antigen and adjuvant provides a transcutaneous delivery system for antigen that can induce an antigen-specific immune response of IgG or IgA. The adjuvant is preferably an ADP-ribosylating exotoxin. Optionally, hydration, penetration enhancers, or occlusive dressings may be used in the transcutaneous delivery system.